In-Operando Neutron Radiography Studies of Polymer Electrolyte Membrane Water Electrolyzers
In this work, operating PEMWE cells are examined using synchrotron X-ray radiography at BESSY II and using neutron radiography at BER II (both Helmholtz-Zentrum Berlin). In both setups, a synchrotron X-ray beam or a neutron beam is directed at the running cell, and the attenuation dependence of the beam on the elements inside the cell allows visualizing the processes occurring inside the cells. Both methods are to a certain degree complimentary – the synchrotron radiography setup allows inspecting small areas of some mm² with a spatial resolution of a few µm, while the neutron radiography allows inspecting areas of several cm² with a spatial resolution of lower than 100µm. The especially strong neutron attenuation in hydrogen offers the possibility to visualize the gas/water distribution on large areas, while the comparably low neutron attenuation in metals allows using a typical cell setup with only minor adjustments.
The PEMWE cells examined using neutron radiography contained different PTLs, which were compared in terms of the gas/water distribution under different operating conditions. On the anode side, an additional injection of oxygen from the bottom of the cell was used to simulate the effects occurring in a scaled cell exhibiting a larger area. This setup allowed examining the dynamics in the transport and quantifying the distribution along the cell area.
In the PEMWE cells examined using synchrotron radiography, oscillations in the gas bubble discharge from the PTL into the flow channel were investigated in terms of their frequency and the gas discharge volumes. Furthermore, the implications of this on the gas transport within the PTL are discussed, and the number of gas bubble discharge sites is correlated with the current density.
Thereby it is demonstrated that both synchrotron X-ray and neutron radiography represent valuable tools to study transport processes and to gain insights into the gas-water distribution inside running PEMWE cells. These results pose important implications for the design of cell components with facilitated gas removal, for the modeling of two-phase flow in PEMWE cells and for the modeling of mass transport losses in PEMWE.
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Fig. 1 a) Neutron radiograph of a full cell with an area of 17.6 cm², showing a meander-shaped flow channel on the anode side with water flow from bottom to top b) Synchrotron radiograph of an individual channel with gas bubbles visible inside the channel